Snowfall shuts the 5 Freeway

After Santa Ana winds and monster-size surf, a blast of cold air overnight Saturday was expected to generate another extreme weather phenomenon in the mountains: thundersnow.

Saturday night, snowfall shut down Interstate 5 near Castaic, the California Highway Patrol reported. The southbound I-5 was closed starting on the northern end of the Grapevine, and the northbound lanes were shut down at Parker Road. Traffic was being diverted to highways 14 and 58. CHP officials could not say how long the closure would last.

The cold and unstable weather brought on the booming spectacle of thundersnow, the rare combination of heavy snow accompanied by thunder and lightning. Mountain temperatures had dipped into the low 20s and teens by 11 p.m.

“It’s one of the coolest things in the atmosphere,” said Mark Moede, a meteorologist with the National Weather Service in San Diego. Isolated pockets of thundersnow rattle in when atmospheric conditions are both very cold and unstable, Moede said. However, “most areas are just going to see regular old snow,” Moede said.

Rain showers and thunderstorms are expected to move through the Southland today, and officials remained concerned that heavy downpours could cause landslides in burned areas.

In the mountains, forecasters predicted 4 to 8 inches of powder above 6,000 feet. Sleet was falling in San Diego County mountains Saturday night, and forecasters expected the snow level to descend to 3,000 feet.

Snow advisories were in effect until early today in Los Angeles, San Bernardino and Ventura counties; the advisory was to last through noon today in Riverside and San Diego counties.

Highway 38, a major road connecting Los Angeles to the Big Bear ski resorts, was closed for several hours Saturday night between Forest Falls and Lake Matthews because of heavy snow that trapped several vehicles, said Caltrans spokeswoman Shelli Lombardo.

Lombardo recommended that motorists bring tire chains to help navigate snowy mountain roads. Conditions change “so quickly up there,” she said.

Part of Highway 18 in the San Bernardino Mountains -- from east of Highway 330 to Big Bear Dam -- remained closed after a rock slide Friday, according to Caltrans.

California Highway Patrol officials had seen no major weather-related traffic snarls as of Saturday evening but reported snow flurries in the Antelope Valley.

San Bernardino Mountain ski resorts rejoiced over the fresh dusting.

“In Southern California, the natural snowstorms are too far in between,” said Chris Riddle, director of marketing for Big Bear Mountain Resorts.

About one-third of the resort’s 26 ski lifts were open, Riddle said, and the slopes were hopping Saturday.

By Tuesday, northeasterly winds will be gusting up to 40 mph across the Cajon Pass and the Grapevine, Moede said.

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susannah.rosenblatt@la

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